Sputtering targets are essential components in the thin film coating industry. They are used as a source of high purity materials, which are released from the target surface as a result of its bombardment with energetic projectile particles such as an ion beam. The particles that are released, in the form of vapours, are subsequently directed towards the surface of a substrate where they are deposited in the form of a thin film of controlled thickness and purity. The most striking characteristic of the sputtering process is its universality. Virtually any material can be a coating candidate since it is passed into the vapour phase by a physical momentum-exchange rather than a chemical or thermal process.
Thin film deposition using sputtering techniques is an essential step in a wide range of applications such as aluminium alloy and refractory metal microcircuit metallization layers, microcircuit insulation layer, transparent conduction electrodes, amorphous optical film for integrated optics devices, piezo-electric transducers, photoconductors and luminescent film for displays, optically addressed memory devices, amorphous bubble memory devices, thin film resistors and capacitors, video discs, solid electrolytes, thin film laser and microcircuit photolithographic mask blanks.
Target materials vary depending on the application. They can be formed of pure metals such as aluminium, copper, iron, silver, chromium, silicon, tantalum, gold, platinum, rhenium; alloys and compounds, such as cadmium sulfate, gallium arsenate, gallium phosphate; a wide range of ceramics such as silica, alumina, silicon carbide; polymers such as PTFE (Teflon™); or even a mosaic of different materials. The performance of the target is strongly dependant on the purity of the target material, its apparent density and microstructure.
Sputtering targets have traditionally been manufactured through the use of different powder metallurgical techniques for the formation of the target plate made of high purity materials, which are subsequently mounted on the target backing material for proper heat management under its final operating conditions. The technique is relatively tedious and requires a number of steps for the powder preparation and densification, followed by powder compaction at room temperature and subsequent sintering to the required high-density level. In certain cases, room temperature compaction is not sufficient to achieve the required density of the final product. In such cases, it is necessary to resort to the considerably more complex and expensive Hot Iso-static Pressing (HIP) sintering techniques.